US20190027726A1 - Long porous separator sheet, method for producing the same, roll, and lithium-ion battery - Google Patents
Long porous separator sheet, method for producing the same, roll, and lithium-ion battery Download PDFInfo
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- US20190027726A1 US20190027726A1 US15/312,916 US201615312916A US2019027726A1 US 20190027726 A1 US20190027726 A1 US 20190027726A1 US 201615312916 A US201615312916 A US 201615312916A US 2019027726 A1 US2019027726 A1 US 2019027726A1
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- separator
- long
- porous
- sheet
- lateral surface
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims description 47
- 229910001416 lithium ion Inorganic materials 0.000 title claims description 41
- 238000004519 manufacturing process Methods 0.000 title claims description 14
- 238000005520 cutting process Methods 0.000 claims description 59
- 238000000034 method Methods 0.000 claims description 55
- 238000004804 winding Methods 0.000 claims description 6
- 238000012545 processing Methods 0.000 abstract description 10
- 239000004760 aramid Substances 0.000 description 31
- 229920003235 aromatic polyamide Polymers 0.000 description 31
- 239000011148 porous material Substances 0.000 description 19
- 238000000576 coating method Methods 0.000 description 13
- 229920005989 resin Polymers 0.000 description 13
- 239000011347 resin Substances 0.000 description 13
- 239000011248 coating agent Substances 0.000 description 11
- 238000005259 measurement Methods 0.000 description 11
- -1 polyethylene Polymers 0.000 description 11
- 239000004698 Polyethylene Substances 0.000 description 10
- 229920000573 polyethylene Polymers 0.000 description 10
- 238000009863 impact test Methods 0.000 description 9
- 239000000463 material Substances 0.000 description 8
- 229920000098 polyolefin Polymers 0.000 description 7
- 238000011156 evaluation Methods 0.000 description 5
- 239000000243 solution Substances 0.000 description 5
- 239000004699 Ultra-high molecular weight polyethylene Substances 0.000 description 3
- 239000011256 inorganic filler Substances 0.000 description 3
- 229910003475 inorganic filler Inorganic materials 0.000 description 3
- 238000004898 kneading Methods 0.000 description 3
- 230000002093 peripheral effect Effects 0.000 description 3
- 229920013716 polyethylene resin Polymers 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- 229920000785 ultra high molecular weight polyethylene Polymers 0.000 description 3
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 2
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 2
- 239000000155 melt Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 239000007773 negative electrode material Substances 0.000 description 2
- 239000004014 plasticizer Substances 0.000 description 2
- 239000007774 positive electrode material Substances 0.000 description 2
- 239000011342 resin composition Substances 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
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- 239000004743 Polypropylene Substances 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- 229910000019 calcium carbonate Inorganic materials 0.000 description 1
- 239000001768 carboxy methyl cellulose Substances 0.000 description 1
- 235000010948 carboxy methyl cellulose Nutrition 0.000 description 1
- 239000008112 carboxymethyl-cellulose Substances 0.000 description 1
- 239000003086 colorant Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000007607 die coating method Methods 0.000 description 1
- 238000003618 dip coating Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- BXKDSDJJOVIHMX-UHFFFAOYSA-N edrophonium chloride Chemical compound [Cl-].CC[N+](C)(C)C1=CC=CC(O)=C1 BXKDSDJJOVIHMX-UHFFFAOYSA-N 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000000945 filler Substances 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 239000011255 nonaqueous electrolyte Substances 0.000 description 1
- 230000035699 permeability Effects 0.000 description 1
- 229920001155 polypropylene Polymers 0.000 description 1
- 238000005381 potential energy Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 238000007639 printing Methods 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 238000007650 screen-printing Methods 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000004528 spin coating Methods 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 238000004154 testing of material Methods 0.000 description 1
- 229920005992 thermoplastic resin Polymers 0.000 description 1
- 230000037303 wrinkles Effects 0.000 description 1
Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/446—Composite material consisting of a mixture of organic and inorganic materials
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/463—Separators, membranes or diaphragms characterised by their shape
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- H01M2/1686—
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H18/00—Winding webs
- B65H18/08—Web-winding mechanisms
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
- B65H35/00—Delivering articles from cutting or line-perforating machines; Article or web delivery apparatus incorporating cutting or line-perforating devices, e.g. adhesive tape dispensers
- B65H35/02—Delivering articles from cutting or line-perforating machines; Article or web delivery apparatus incorporating cutting or line-perforating devices, e.g. adhesive tape dispensers from or with longitudinal slitters or perforators
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- H01M2/145—
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- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/403—Manufacturing processes of separators, membranes or diaphragms
- H01M50/406—Moulding; Embossing; Cutting
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/411—Organic material
- H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
- H01M50/417—Polyolefins
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
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- H01M50/423—Polyamide resins
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
- H01M50/491—Porosity
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
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- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
- H01M50/494—Tensile strength
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Definitions
- the present invention relates to (i) a long porous separator sheet which has been slit so as to be used in a battery such as a lithium-ion battery, (ii) a method for producing the long porous separator sheet, (iii) a porous separator roll prepared by winding the long porous, separator sheet on a core, and (iv) a lithium-ion battery including a porous separator which has been obtained fay cutting the long porous separator sheet in a predetermined length.
- a separator original sheet used for a lithium-ion battery is slit (cut) in a lengthwise direction of the original sheet, and it is thus possible to obtain a plurality of long separator sheets each of which has a predetermined slit width in a direction perpendicular to the lengthwise direction.
- Each of the plurality of long separator sheets is wound on a core and is then supplied to a battery production process as a separator roll.
- each of the plurality of long separator sheets is cut in a predetermined length in a direction perpendicular to the slit width, and is thus used as a separator.
- a lateral surface itself of the long separator sheet which has been obtained by slitting serves as a lateral surface of a battery separator, and therefore a shape of the lateral surface is important.
- Patent Literature 1 discloses a separator which includes a base material layer and an inorganic layer and has a lateral surface that is formed into a taper shape in order to inhibit the inorganic layer from being peeled off from the base material layer in a case where the separator is bent.
- Patent Literature 2 discloses that a photosensitive material is cut with a shear cutting method so that a lateral surface thereof lies at a right angle.
- a separator is provided between a positive electrode and a negative electrode and is wound, together with the positive electrode and the negative electrode, in a machine direction (MD: a lengthwise direction of a long separator sheet). Further, the positive electrode material, the negative electrode material, and the separator which have been wound are inserted into a cylindrical container. Therefore, with regard to the positive electrode material, the negative electrode material, and the separator which have been wound and inserted into the cylindrical container, a lateral surface of a battery separator, which surface corresponds to a slit lateral surface of the long separator sheet, is exposed.
- a separator In a laminated-type battery, a separator is to be placed on a positive electrode or a negative electrode so as to cover the positive electrode or the negative electrode. Therefore, as with a case of the wound-type battery, a lateral surface of a battery separator, which surface corresponds to a slit lateral surface of the long separator sheet, is exposed.
- the slit lateral surface of the long separator sheet is also exposed.
- Patent Literature 2 merely discloses that a non-porous material is cut with a shear cutting method so that both lateral surfaces thereof lie at a right angle, and straightness of a lateral surface of such a non-porous material is not so important because the straightness of the non-porous material is high in the first place, unlike a porous material such as a separator.
- a lateral surface of the long porous separator sheet has a value of R/P that is less than 1.04, where P is a linear distance between two points on a straight line in a lengthwise direction in an image of the lateral surface, and R is a distance along a shape of the lateral surface between the two points on the straight line in the lengthwise direction, the linear distance P and the distance R being obtained by binarizing the image between the long porous separator sheet and a part other than the long porous separator sheet.
- the method of the present invention for producing a long porous separator sheet includes the step of slitting a porous separator original sheet in a lengthwise direction of the porous separator original sheet, the slitting step including forming a lateral surface of the long porous separator sheet with use of a slitting section including an tipper blade and a lower blade which rotate in different directions, the upper blade making contact with one of two lower blades in a space formed between the two lower blades which are adjacent in a transverse direction that is perpendicular to the lengthwise direction.
- FIG. 1 is a schematic view illustrating a cross sectional configuration of a lithium-ion secondary battery.
- FIG. 3 is a schematic view illustrating another configuration of the lithium-ion secondary battery illustrated in FIG. 1 .
- FIG. 4 is a schematic view illustrating a configuration of a slitting apparatus for slitting a separator original sheet
- (b) of FIG. 4 is a view illustrating a state in which the separator original sheet is slit into a plurality of long separator sheets by the slitting apparatus.
- FIG. 5 is a view illustrating a cutting device which operates in a shear cutting mode and is provided in the slitting apparatus illustrated in FIG. 4
- (b) of FIG. 5 is a view illustrating a slitting section which is provided in the cutting device that operates in the shear cutting mode
- (c) of FIG. 5 is a view illustrating a state in which a separator original sheet is slit by the slitting section.
- FIG. 6 is a view illustrating a part of a lateral surface of a long separator sheet in which part straightness is evaluated.
- FIG. 7 is a view for explaining a cutting method carried out with a razor blade.
- FIG. 8 is a view for explaining a method for evaluating straightness of a lateral surface of a long separator sheet
- (b) and (c) of FIG. 8 are views showing evaluation results of the straightness.
- FIG. 9 is a schematic view illustrating straightness of a lateral surface of a long separator sheet in accordance with the present embodiment
- (b) of FIG. 9 is a schematic view illustrating straightness of a lateral surface of a long separator sheet which has been slit with a razor cutting method.
- FIG. 10 is a view for explaining (i) a method for measuring tensile strength of a specimen whose one lateral surface is a lateral surface of a long porous separator sheet made of polyethylene and (ii) results of the measurement.
- FIG. 11 is a view for explaining (i) a measuring method in the Charpy impact test carried out on a specimen whose one lateral surface is a lateral surface of a long porous separator sheet made of polyethylene and (ii) results of the measurement.
- a nonaqueous electrolyte secondary battery typically, a lithium-ion secondary battery has a high energy density, and therefore, currently widely used not only as batteries for use in devices such as personal computers, mobile phones, and mobile information terminals, and for use in moving bodies such as automobiles and airplanes, but also as stationary batteries contributing to stable power supply.
- FIG. 1 is a schematic view illustrating a cross sectional configuration of a lithium-ion secondary battery 1 .
- the lithium-ion secondary battery 1 includes a cathode 11 , a separator 12 , and an anode 13 . Between the cathode 11 and the anode 13 , an external device 2 is connected outside the lithium-ion secondary battery 1 . While the lithium-ion secondary battery 1 is being charged, electrons move in a direction A. On the other hand, while the lithium-ion secondary battery 1 is being discharged, electrons move in a direction B.
- the separator 12 is provided so as to be sandwiched between the cathode 11 which is a positive electrode of the lithium-ion secondary battery 1 and the anode 13 which is a negative electrode of the lithium-ion secondary battery 1 .
- the separator 12 is a porous film that separates the cathode 11 and the anode 13 , allowing lithium ions to move between the cathode 11 and the anode 13 .
- the separator 12 contains, for example, polyolefin such as polyethylene or polypropylene as a material.
- the separator 12 is provided with many pores P. Normally, lithium ions 3 in the lithium-ion secondary battery 1 can move back and forth through the pores P.
- the separator 12 melts or softens and the pores P are blocked as illustrated in (b) of FIG. 2 . As a result, the separator 12 shrinks. This stops the movement of the lithium ions 3 , and consequently slops the above described temperature rise.
- FIG. 3 is a schematic view illustrating another configuration of the lithium-ion secondary battery 1 illustrated in FIG. 1 .
- (a) of FIG. 3 illustrates a normal configuration
- (b) of FIG. 3 illustrates a state in which a temperature of the lithium-ion secondary battery 1 has sharply risen.
- the separator 12 can be a heat resistant separator that includes a porous film 5 and a heat resistant layer 4 .
- the heat resistant layer 4 is laminated on a surface of the porous film 5 which surface is on a cathode 11 side.
- the heat resistant layer 4 can alternatively be laminated on a surface of the porous film 5 which surface is on an anode 13 side, or both surfaces of the porous film 5 .
- the heat resistant layer 4 is provided with, pores which are similar to the pores P. Normally, the lithium ions 3 move through the pores P and the pores of the heat resistant layer 4 .
- the heat resistant layer 4 contains, for example, wholly aromatic polyamide (aramid resin) as a material.
- the heat resistant separator can be produced by a well-known method.
- the following discussion assumes a case where the porous film 5 contains polyethylene as a main material. However, even in a case where the porous film 5 contains another material, the similar steps can still be applied to production of the separator 12 .
- the porous film 5 is made of a polyethylene resin containing ultrahigh molecular weight polyethylene, it is possible to produce the porous film 5 by the following method.
- This method includes (1) a kneading step of obtaining a polyethylene resin composition by kneading a ultrahigh molecular weight polyethylene and an inorganic filler such as calcium carbonate, (2) a roiling step of forming a film with the polyethylene resin composition, (3) a removal step of removing the inorganic filler from the film obtained in the step (2), and (4) a stretching step of obtaining the porous film 5 by stretching the film obtained in the step (3).
- the ultrahigh molecular weight polyethylene 100 parts by weight of the ultrahigh molecular weight polyethylene, 5 parts by weight to 200 parts by weight of a low-molecular weight polyolefin having a weight-average molecular weight of 10000 or less, and 100 parts by weight to 400 parts by weight of the inorganic filler can be kneaded.
- the heat resistant layer 4 is formed on a surface of the porous film 5 .
- an aramid/NMP (N-methylpyrrolidone) solution (coating solution) is applied, and thereby the heat resistant layer 4 that is an aramid heat resistant layer is formed.
- the heat resistant layer 4 can be provided on only one surface or both surfaces of the porous film 5 .
- the heat resistant layer 4 can be formed by using a mixed solution containing a filler such as alumina/carboxymethyl cellulose.
- a method for coating the porous film 5 with a coating solution is not specifically limited as long as uniform wet coating can be carried out by the method.
- the method can be a conventionally well-known method such as a capillary coating method, a spin coating method, a slit die coating method, a spray coating method, a dip coating method, a roll coating method, a screen printing method, a flexo printing method, a bar coater method, a gravure coater method, or a die coater method.
- the heat resistant layer 4 has a thickness which can be controlled by adjusting (i) a thickness of a coating wet film and (ii) a solid-content concentration in the coating solution.
- the separator 12 heat resistant separator
- the heat resistant layer 4 is laminated on the porous film 5 .
- the separator is wound on a cylindrical core.
- a subject to be produced by the above production method is not limited to the heat resistant separator.
- the above production method does not necessarily include the coating step. In a case where the method includes no coating step, the subject to be produced is a separator including no heat resistant layer.
- the heat resistant separator or the separator including no heat resistant layer (hereinafter, referred to as “separator”) preferably has a width (hereinafter, referred to as “product width”) suitable for application products such as the lithium-ion secondary battery 1 .
- product width a width suitable for application products such as the lithium-ion secondary battery 1 .
- the separator is produced so as to have a width that is equal to or larger than a product width. This is referred to as a separator original sheet.
- the separator original sheet is cut (slit) by the slitting apparatus so that a “separator width” (which means a length in a direction substantially perpendicular to a lengthwise direction and a thickness direction) of the separator original sheet becomes the product width, and thus a long separator sheet is obtained.
- a “separator width” which means a length in a direction substantially perpendicular to a lengthwise direction and a thickness direction
- a wide separator which is before being slit is referred to as “separator original sheet”, and a separator which has been slit so as to have a separator width that is the product width is particularly referred to as “long separator sheet”.
- slitting means to slit the separator original sheet in the lengthwise direction (i.e., a flow direction of the film during production; MD: machine direction), and that “cutting” means to cut the long separator sheet in a transverse direction (TD).
- the “transverse direction (TD)” means a direction which is substantially perpendicular to the lengthwise direction (MD) and the thickness direction of the long separator sheet.
- FIG. 4 is a schematic view illustrating a configuration of a slitting apparatus 6 which includes a cutting device 7 that operates in a shear cutting mode.
- (b) of FIG. 4 is a view illustrating a state in which an original sheet 12 O of a separator (porous separator) is slit into long separator sheets (long porous separator sheets) 12 a and 12 b by the slitting apparatus 6 .
- Embodiment 1 exemplifies the separator original sheet 12 O in which a wholly aromatic polyamide (aramid resin) as the heat resistant layer 4 is laminated on one surface of the porous film 5 , as illustrated in FIG. 3 .
- the separator original sheet 12 O can be a porous film 5 on which no heat resistant layer 4 is laminated or can be a sheet in which heat resistant layers 4 are laminated on both surfaces of the porous film 5 .
- the slitting apparatus 6 includes a wind-off roller 63 which is rotatably supported and has a cylindrical shape, rollers 64 , 65 , 68 U, 68 L, 69 U, and 69 L, a first touch roller 81 U, a second touch roller 81 L, a first arm 82 U, a second arm 82 L, a first take-up assisting roller 83 U, a second take-up assisting roller 83 L, a first winding-up roller 70 U, a second winding-up roller 70 L, and the cutting device 7 .
- a wind-off roller 63 which is rotatably supported and has a cylindrical shape, rollers 64 , 65 , 68 U, 68 L, 69 U, and 69 L, a first touch roller 81 U, a second touch roller 81 L, a first arm 82 U, a second arm 82 L, a first take-up assisting roller 83 U, a second take-up assisting roller 83 L,
- a cylindrical core c is attached onto the wind-off roller 63 , and the separator original sheet 12 O is wound on the core c.
- the separator original sheet 12 O is wound off from the core c along a route U or L.
- the separator original sheet 12 O is wound off along the route L.
- the separator original sheet 12 O is wound off along the route U.
- the separator original sheet 12 O is transferred while the surface A serves as an upper surface, and therefore the separator original sheet 12 O is wound off along the route L.
- the surface A is a surface of the porous film 5 which surface is opposite to a surface making contact with the heat resistant layer 4
- the surface B is a surface of the heat resistant layer 4 which surface is opposite to a surface making contact with the porous film 5 .
- the separator original sheet 12 O which has been thus wound off is transferred to the cutting device 7 via the roller 64 and the roller 65 , and is then slit into long separator sheets 12 a and 12 b by the cutting device 7 (see (a) and (b) of FIG. 4 ).
- FIG. 5 is a view illustrating the cutting device 7 which operates in a shear cutting mode and is provided in the slitting apparatus 6 illustrated in FIG. 4 .
- (b) of FIG. 5 is a view illustrating a slitting section S provided in the cutting device 7 .
- (c) of FIG. 5 is a view illustrating a state in which the separator original sheet 12 O is slit by the slitting section S of the cutting device 7 .
- the cutting device 7 which operates in a shear cutting mode includes a shaft 66 and a shaft 67 each of which has a cylindrical shape.
- the shaft 66 and the shaft 67 are supported so as to rotate in different directions and are located on a lower side and on an upper side, respectively.
- the shaft 67 which is on the upper side is provided with a plurality ( 8 in Embodiment 1) of upper blades 67 a each of which is a circular blade.
- the plurality of upper blades 67 a each of which is a circular blade are inserted into respective of a plurality ( 8 in Embodiment 1) of spaces which are provided in the shaft 66 located on the lower side.
- the cutting device 7 which operates in the shear cutting mode includes a plurality ( 8 in Embodiment 1) of slitting sections S.
- each of the slitting sections S which are provided in the cutting device 7 that operates in the shear cutting mode, includes (i) the upper blade 67 a, (ii) lower blades 66 a which are adjacent to each other in the transverse direction (TD) that is perpendicular to the lengthwise direction (MD), and (iii) a space 66 b that is provided between the lower blades 66 a which are adjacent, to each other.
- the lower blades 66 a and the space 66 b are provided in the shaft 66 that is located on the lower side.
- the upper blade 67 a is inserted into the space 66 b and makes contact with a lateral surface of one of the adjacent two lower blades 66 a which one is located on a left side in (c) of FIG. 5 .
- An edge part of the upper blade 67 a has a flat part 67 b and an inclined part 67 c.
- the flat part 67 b is a part which is to make contact with the lower blade 66 a.
- the inclined part 67 c is opposite to the flat part 67 b and is inclined so that, the edge part of the upper blade 67 a gradually becomes sharper toward a tip of the upper blade 67 a.
- Embodiment 1 an example is described in which the edge part of the upper blade 67 a has a cross section in which only one side is inclined but the edge part of the upper blade 67 a can have a cross section of a rocking shear, or the like.
- each of the long separator sheets 12 a and 12 b is to have (i) a lateral surface 12 c that is shaped by the tipper blade 67 a (specifically, the inclined part 67 c of the upper blade 67 a ) and the space 66 b and (ii) a lateral surface 12 d that is shaped by the upper blade 67 a (specifically, the flat part 67 b of the tipper blade 67 a ) and the lower blade 66 a with which the upper blade 67 a contacts.
- Embodiment 1 in order to inhibit, the heat resistant layer 4 from being peeled off, the upper blade 67 a. is brought into contact with the surface A, i.e., the surface of the porous film 5 which surface is opposite to the surface making contact with the heat resistant layer 4 . Note, however, that Embodiment 1 is not limited to this.
- an angle at which the upper blade 67 a makes contact with the lower blade 66 a and a pressure with which the upper blade 67 a makes contact with the lower blade 66 a can be appropriately adjusted to he an angle and a pressure which are suitable for producing the long separator sheets 12 a and 12 b.
- each of the long separator sheets 12 a is transferred via the roller 68 U, the roller 69 U, and the first take-up assisting roller 83 U, and is then wound on a cylindrical core u (bobbin) that is attached onto the first winding-up roller 70 U.
- each of the long separator sheets 12 b among the plurality of long separator sheets 12 a and 12 b is transferred via the roller 68 L, the roller 69 L, and the second take-up assisting roller 83 L, and is then wound on a cylindrical core 1 (bobbin) that is attached onto the second winding-up roller 70 L,
- the long separator sheets 12 a and 12 b which have been wound in rolls are referred to as separator rolls 12 U and 12 L.
- the long separator sheets 12 a and 12 b are wound so that the surface A of each of the long separator sheets 12 a and 12 b faces outside and the surface B of each of the long separator sheets 12 a and 12 b faces inside.
- the separator original sheet 12 O is slit, into seven long separator sheets 12 a and 12 b (slitting step) by the eight slitting sections S in the transverse direction (TD) and along the lengthwise direction (MD).
- four odd-numbered long separator sheets 12 a and three even-numbered long separator sheets 12 b are obtained.
- the four odd-numbered long separator sheets 12 a are wound on the respective cylindrical cores u (bobbin) which are attached onto the first winding-up roller 70 U, and the three even-numbered long separator sheets 12 b are wound on the respective cylindrical cores 1 (bobbin) which are attached onto the second winding-up roller 70 L.
- Embodiment 1 is not limited to this example, and it is of course possible to appropriately change the number of the long separator sheets 12 a and 12 b into which the separator original sheet 12 O is slit, because the number of the long separator sheets 12 a and 12 b depends on a size of the separator original sheet 12 O and a separator width of each of the long separator sheets 12 a and 12 b. Note that, in Embodiment 1, long separator sheets which are obtained on both ends by the slitting with use of the eight slitting sections S are not used.
- Embodiment 1 an example is described in which the number of long separator sheets that are wound on the respective cylindrical cores u (bobbin) provided on the first winding-up roller 70 U is different from the number of long separator sheets that are wound on the respective cylindrical cores 1 (bobbin) provided on the second winding-tip roller 70 L. Note, however, that the number of long separator sheets that are wound on the respective cylindrical cores u can be identical with the number of long separator sheets that are wound on the respective cylindrical cores 1 .
- first winding-up roller 70 U On the first winding-up roller 70 U (winding-up section), four cores u are detachably provided in accordance with the number of the long separator sheets 12 a, i.e., the four odd-numbered long separator sheets 12 a.
- second winding-up roller 70 L On the second winding-up roller 70 L (winding-up section), three cores 1 are detachably provided in accordance with the number of the long separator sheets 12 b, i.e., the three even-numbered long separator sheets 12 b.
- the first winding-up roller 70 U rotates in a direction indicated by the arrow in (a) of FIG. 4 together with the core u so as to wind up the long separator sheet 12 a (winding-up step).
- the core u can be detached from the first winding-up roller 70 U together with the long separator sheet 12 a which has been wound on the core u.
- the second winding-up roller 70 L rotates in a direction indicated by the arrow in (a) of FIG. 4 together with the core 1 so as to wind up the long separator sheet 12 b (winding-up step).
- the core 1 can be detached from the second winding-up roller 70 L together with the long separator sheet 12 b which has been wound on the core 1 .
- the first touch roller 81 U in the slitting apparatus 6 is rotatably provided at (i.e., fixed to) one end of the first arm 82 U
- the second touch roller 81 L in the slitting apparatus 6 is rotatably provided at (i.e., fixed to) one end of the second arm 82 L
- the first arm 82 U can swing on a rotary shaft 84 U (shaft) that is provided at the other end of the first arm 82 U
- the second arm 82 L can swing on a rotary shaft 84 L (shaft) that is provided at the other end of the second arm 82 L (in respective directions indicated by arrows in (a) of FIG. 4 ).
- the first take-up assisting roller 83 U is provided between the first touch roller 81 U and the rotary shaft 84 U of the first arm 82 U and is rotatably fixed to the first arm 82 U.
- the second take-tip assisting roller 83 L is provided between the second touch roller 81 L and the rotary shaft 84 L of the second arm 82 L and is rotatably fixed to the second arm 82 L.
- first and second touch rollers 81 U and 81 L press the long separator sheets 12 a and 12 b, which are to be wound up, onto winding-up surfaces (surfaces) of the separator rolls 12 U and 12 L, respectively.
- the first and second touch rollers 81 U and 81 L press the respective long separator sheets 12 a and 12 b by utilizing weights of the first and second touch rollers 81 U and 81 L, respectively.
- the pressing by the first and second touch rollers 81 U and 81 L makes it possible to inhibit a wrinkle and the like from occurring in the long separator sheets 12 a and 12 b to be wound.
- positions of the first and second touch rollers 81 U and 81 L change (displace) in accordance with change in outer diameters of the separator rolls 12 U and 12 L such that the first and second touch rollers 81 U and 81 L make contact with the winding-up surfaces, respectively.
- FIG. 6 is a view illustrating a part of a lateral surface of each of the long separator sheets 12 a and 12 b in which part straightness is evaluated.
- Embodiment 1 as illustrated in (a) of FIG. 6 , straightness of the lateral surface 12 c (indicated by A in (a) of FIG. 6 ) of each of the long separator sheets 12 a and 12 b was evaluated. Specifically, straightness of a part of the lateral surface 12 c which part makes contact with the surface B was evaluated.
- This part corresponds of an edge part (indicated by A in (b) of FIG. 6 ) of the separator rolls 12 U and 12 L, and also corresponds to a part A of each of the long separator sheets 12 a and 12 b illustrated in (c) of FIG. 6 .
- FIG. 7 is a view for explaining a conventional cutting (slitting) method carried out with a razor blade.
- the separator original sheet 12 O is transferred to a roller 101 .
- the roller 101 has a groove into which an edge of a razor blade 100 can be partially inserted. With the configuration, the separator original sheet 12 O is slit into long separator sheets by the razor blade 100 and the groove.
- FIG. 8 is a view for explaining a method for evaluating straightness of a lateral surface of a long separator sheet.
- (b) of FIG. 8 is a view showing results of straightness evaluation on a lateral surface of a long separator sheet (here, referred to as “polyolefin separator”) which has been obtained by slitting the porous film 5 , which has no heat resistant layer 4 , with the shear cutting method illustrated in FIG. 5 .
- polyolefin separator here, referred to as “polyolefin separator”
- FIG. 8 is a view showing results of straightness evaluation on the lateral surface 12 c of each of the long separator sheets 12 a and 12 b (here, referred to as laminated separator) which has been obtained by slitting the separator original sheet 12 O, in which wholly aromatic poly amide (aramid resin) is laminated as the heat resistant layer 4 on one surface of the porous film 5 , with the razor cutting method illustrated in FIG. 7 and the shear cutting method illustrated in FIG. 5 .
- laminated separator wholly aromatic poly amide (aramid resin)
- a lower part of the original image illustrated in (a) of FIG. 8 is a surface B side of each of the long separator sheets 12 a and 12 b illustrated in (a) of FIG. 6 .
- the original image is binarized into each of the long separator sheets 12 a and 12 b and a part other than each of the long separator sheets 12 a and 12 b.
- each of the Jong separator sheets 12 a and 12 b can be distinguished from the part other than each of the long separator sheets 12 a and 12 b.
- the part other than each of the long separator sheets 12 a and 12 b has a peripheral length (O+P+Q+R) including a left side length. (O), a longer side length (P), a right side length (Q), and an edge length (R).
- the longer side length (P) corresponds to a linear distance between two points on a straight line along the MD on the lateral surface 12 c
- the edge length (R) corresponds to a distance which is along a shape of the lateral surface 12 c between the two points on the straight line along the MD.
- edge length (R)/longer side length (P) In a case where the value of “edge length (R)/longer side length (P)” is large, this means that distortion in a direction perpendicular to the MD is large. Meanwhile, in a case where the value is small, this means that distortion in the direction perpendicular to the MD is small.
- edge length (R)/longer side length (P) needs to be less than 1.04.
- the value of “edge length (R)/longer side length (P)” was 1.047, which was greatly different from the ideal value, i.e., 1 (see (c) of FIG. 8 ).
- the long separator sheet which is obtained by slitting the separator original sheet 12 O, in which wholly aromatic polyamide (aramid resin) is laminated as the heat resistant layer 4 on one surface of the porous film 5 , with the razor cutting method illustrated in FIG. 7 is not preferable.
- FIG. 9 is a schematic view illustrating the straightness of the lateral surface 12 c of each of the long separator sheets 12 a and 12 b (laminated separator) which has been obtained by slitting the separator original sheet 12 O, in which wholly aromatic polyamide (aramid resin) is laminated as the heat resistant layer 4 on one surface of the porous film 5 , with the shear cutting method illustrated in FIG. 5 .
- FIG. 9 is a schematic view illustrating the straightness of a lateral surface 12 c ′ of each of long separator sheets 12 a ′ and 12 b ′ (laminated separator) which has been obtained by slitting the separator original sheet 12 O, in which wholly aromatic polyamide (aramid resin) is laminated as the heat resistant layer 4 on one surface of the porous film 5 , with the razor cutting method illustrated in FIG. 7 .
- wholly aromatic polyamide aramid resin
- the long separator sheets 12 a and 12 b having the high straightness of the lateral surface are more preferable than the long separator sheets 12 a ′ and 12 b ′ having the low straightness of the lateral surface.
- FIG. 10 is a view for explaining (i) a method for measuring tensile strength of a specimen 12 e whose one lateral surface is a lateral surface 12 c ′′ of each of the long separator sheets 12 a ′′ and 12 b ′′ which are wound into respective separator rolls 12 U′′ and 12 L′′.
- the separator rolls 12 U′′ and 12 L′′ illustrated, in (a) of FIG. 10 are obtained by winding 200 m of the respective long separator sheets 12 a ′′ and 12 b ′′ on respective cores u and l having a diameter of 3 inches.
- the long separator sheets 12 a ′′ and 12 b ′′ have been obtained by slitting a separator original sheet, in which wholly aromatic polyamide as a heat resistant layer is laminated on one surface of a porous film made of polyethylene, in a lengthwise direction (MD) of the original sheet.
- the specimen 12 e has been prepared by cutting, with use of a cutter, out from each of the long separator sheets 12 a ′′ and 12 b ′′ so as to include, as one lateral surface, the lateral surface 12 c ′′ of each of the long separator sheets 12 a ′′ and 12 b ′′ and to have a size of 1 cm (width) ⁇ 5 cm (length).
- upper and lower parts (each having a length of 1.5 cm) of the specimen 12 e are placed on respective chucks (holding base) 14 a and 14 b , and a distance between the chuck 14 a and the chuck 14 b is 2 cm.
- a tensile strength X (MPa) was calculated from a stress A (N) with which the specimen 12 e was torn. Specifically, the tensile strength X (MPa) was calculated based on the following (Formula 1):
- an average tensile strength X (MPa) of the specimens is 2.12 Mpa
- an average tensile strength X (MPa) of the specimens 12 e is 224 Mpa. From these results, the tensile strength of the specimens 12 e each having the lateral surface obtained by slitting with the shear cutting is evidently larger than the tensile strength of the specimens each having the lateral surface obtained by slitting with the razor cutting method.
- a larger tensile strength means to be tougher against stretching.
- concentration of stress occurs in stretching, and accordingly breaking may be more likely to occur.
- FIG. 11 is a view for explaining (i) a measuring method in the Charpy impact test on a specimen 12 f whose one lateral surface is a lateral surface 12 c ′′ of each of the long separator sheets 12 a ′′ and 12 b ′′ which are wound into respective separator rolls 12 U′′ and 12 L′′.
- the separator rolls 12 U′′ and 12 L′′ illustrated in (a) of FIG. 11 are obtained by winding 200 m of the respective long separator sheets 12 a ′′ and 12 b ′′ on respective cores u and l having a diameter of 3 inches.
- the long separator sheets 12 a ′′ and 12 b ′′ have been obtained by slitting a separator original sheet, in which wholly aromatic polyamide as a heat resistant layer is laminated on one surface of a porous film made of polyethylene, in a lengthwise direction (MD) of the original sheet.
- the specimen 12 f has been prepared by cutting, with use of a cutter, out from each of the long separator sheets 12 a ′′ and 12 b ′′ so as to include, as one lateral surface, the lateral surface 12 c ′′ of each of the long separator sheets 12 a ′′ and 12 b ′′ and to have a size of 1 cm (width) ⁇ 8 cm (length).
- a notch is provided in a specimen for the Charpy impact test.
- a shape itself of a slit edge part of a specimen is evaluated, and therefore no notch is additionally provided in the sample which has been cut out in a rectangular shape.
- FIG. 11 is a schematic view for explaining a measuring method in the Charpy impact test on the specimen 12 f
- (c) of FIG. 11 is a view showing results of the Charpy impact test on the specimen 12 f.
- a pendulum (hammer) 15 which is heavy is swung down onto the specimen 12 f from a height h′, and then the pendulum 15 breaks the specimen 12 f and is then swung up to a height h.
- a distance k is a distance between a rotation center of the pendulum 15 and a center of gravity of the pendulum 15 .
- An angle ⁇ in (b) of FIG. 11 does not change in accordance with replacement of the specimen, and indicates a lifting angle. Meanwhile, an angle ⁇ in (b) of FIG. 11 is an angle of the pendulum 15 .
- the angle ( ⁇ ) of the pendulum 15 becomes smaller when energy consumed to break the specimen is larger, and the angle ( ⁇ ) of the pendulum 15 becomes larger when energy consumed to break the specimen is smaller.
- the pendulum 15 is swung down from the predetermined height h′ regardless of types of the specimen, and therefore initial energy (potential energy) of the pendulum 15 is constant. From this, the angle ( ⁇ ) of the pendulum 15 represents residual energy obtained by subtracting, from the initial energy, energy consumed to break the specimen.
- an average angle ( ⁇ ) of the pendulum 15 in the 5-time trials was 114.9° in regard to the specimens (edge length (R)/longer side length (P): 1.000) which had been obtained from the long separator sheet obtained by slitting, with the shear cutting method, the separator original sheet in which wholly aromatic polyamide as the heat resistant layer was laminated on one surface of the porous film made of polyethylene.
- an average angle ( ⁇ ) of the pendulum 15 in the 5-time trials was 117.4° in regard to the specimens (edge length (R)/longer side length (P): 1.047) which had been obtained from the long separator sheet obtained by slitting, with the razor cutting method, the separator original sheet in which wholly aromatic polyamide as the heat resistant layer was laminated on one surface of the porous film made of polyethylene.
- a lateral surface of the long porous separator sheet has a value of R/P that is less than 1.04, where P is a linear distance between two points on a straight line in a lengthwise direction in an image of the lateral surface, and R is a distance along a shape of the lateral surface between the two points on the straight line in the lengthwise direction, the linear distance P and the distance R being obtained by binarizing the image between the long porous separator sheet and a part other than the long porous separator sheet.
- the value of R/P of the lateral surface of the long porous separator sheet is less than 1.04.
- the straightness of the lateral surface is high even though the long porous separator sheet is made of a porous material, and it is therefore possible to reduce a possibility that the long separator sheet is torn in processing.
- the long porous separator sheet in accordance with an aspect 2 of the present invention can include, in the aspect 1, a plurality of layers.
- the long porous separator sheet which is made up of a plurality of layers.
- the plurality of layers are a porous film layer and a porous heat resistant layer which is laminated on one surface of the porous film layer.
- the plurality of layers are a porous film layer and porous heat resistant layers which are laminated on both surfaces of the porous film layer.
- the lateral surface of the long porous separator sheet is obtained by being slit in a slitting section including an upper blade and a lower blade which rotate in different directions, the upper blade making contact with one of two lower blades in a space formed between the two lower blades which are adjacent in a transverse direction that is perpendicular to the lengthwise direction.
- the porous separator roll in accordance with an aspect 6 of the present invention is configured by winding, on a core, the long porous separator sheet described in any one of the aspects 1 through 5.
- the porous separator roll obtained by winding, on a core, the long porous separator sheet whose lateral surface has high straightness.
- the lithium-ion battery in accordance with an aspect 7 of the present invention is configured to include a porous separator which has been obtained by cutting, in a predetermined length, the long porous separator sheet described in any one of the aspects 1 through 5 in a transverse direction that is perpendicular to the lengthwise direction.
- the lithium-ion battery which includes the porous separator whose lateral surface has high straightness.
- the method in accordance with an aspect 8 of the present invention for producing a long porous separator sheet includes the step of slitting a porous separator original sheet in a lengthwise direction of the porous separator original sheet, the slitting step including forming a lateral surface of the long porous separator sheet with use of a slitting section including an upper blade and a lower blade which rotate in different directions, the upper blade making contact with one of two lower blades in a space formed between the two lower blades which are adjacent in a transverse direction that is perpendicular to the lengthwise direction.
- the method it is possible to form the lateral surface of the long porous separator sheet whose straightness is high even though the long porous separator sheet is made of a porous material. It is therefore possible to reduce a possibility that the long separator sheet is torn in processing.
- the present invention is not limited to the embodiments, but can be altered by a skilled person in the art within the scope of the claims.
- An embodiment derived from a proper combination of technical means each disclosed in a different embodiment is also encompassed in the technical scope of the present invention. Further, it is possible to form a new technical feature by combining the technical means disclosed in the respective embodiments.
Abstract
Description
- The present invention relates to (i) a long porous separator sheet which has been slit so as to be used in a battery such as a lithium-ion battery, (ii) a method for producing the long porous separator sheet, (iii) a porous separator roll prepared by winding the long porous, separator sheet on a core, and (iv) a lithium-ion battery including a porous separator which has been obtained fay cutting the long porous separator sheet in a predetermined length.
- A separator original sheet used for a lithium-ion battery is slit (cut) in a lengthwise direction of the original sheet, and it is thus possible to obtain a plurality of long separator sheets each of which has a predetermined slit width in a direction perpendicular to the lengthwise direction.
- Each of the plurality of long separator sheets is wound on a core and is then supplied to a battery production process as a separator roll. In the battery production process, each of the plurality of long separator sheets is cut in a predetermined length in a direction perpendicular to the slit width, and is thus used as a separator.
- As such, a lateral surface itself of the long separator sheet which has been obtained by slitting serves as a lateral surface of a battery separator, and therefore a shape of the lateral surface is important.
- In view of this,
Patent Literature 1 discloses a separator which includes a base material layer and an inorganic layer and has a lateral surface that is formed into a taper shape in order to inhibit the inorganic layer from being peeled off from the base material layer in a case where the separator is bent. - Meanwhile,
Patent Literature 2 discloses that a photosensitive material is cut with a shear cutting method so that a lateral surface thereof lies at a right angle. - [Patent Literature 1]
- Japanese Patent Application Publication Tokukai No. 2012-199020 (Publication date: Oct. 18, 2012)
- [Patent Literature 2]
- Japanese Patent Application Publication Tokukai No. 2005-66796 (Publication date: Mar. 17, 2005)
- In a wound-type battery, a separator is provided between a positive electrode and a negative electrode and is wound, together with the positive electrode and the negative electrode, in a machine direction (MD: a lengthwise direction of a long separator sheet). Further, the positive electrode material, the negative electrode material, and the separator which have been wound are inserted into a cylindrical container. Therefore, with regard to the positive electrode material, the negative electrode material, and the separator which have been wound and inserted into the cylindrical container, a lateral surface of a battery separator, which surface corresponds to a slit lateral surface of the long separator sheet, is exposed.
- In a laminated-type battery, a separator is to be placed on a positive electrode or a negative electrode so as to cover the positive electrode or the negative electrode. Therefore, as with a case of the wound-type battery, a lateral surface of a battery separator, which surface corresponds to a slit lateral surface of the long separator sheet, is exposed.
- Moreover, while a battery is being assembled, the slit lateral surface of the long separator sheet is also exposed.
- In a case where straightness of the slit lateral surface of the long separator sheet, or the lateral surface of the battery separator, which surfaces are exposed while the battery is being assembled, is low, the long separator sheet or the battery separator is more likely to be caught on something and may accordingly be torn.
- Note that the straightness of the slit lateral surface of the long separator sheet or the lateral surface of the battery separator is represented by a value of R/P, where P is a linear distance between two points on a straight line along the MD on each of the lateral surfaces, and R is a distance along a shape of the lateral surface between the two points on the straight line along the MD. In a case where the value of R/P is large, this means that distortion in a direction perpendicular to the MD is large. Meanwhile, in a case where the value of R/P is small, this means that distortion in the direction perpendicular to the MD is small.
- Therefore, the straightness of the slit lateral surface of the long separator sheet and the lateral surface of the battery separator is important.
- However,
Patent Literature 1 merely discloses that both lateral surfaces of the separator are formed into the taper shape in order to inhibit the inorganic layer from being peeled off from the base material layer and does not give attention to straightness of the lateral surface of the separator at all. - Moreover,
Patent Literature 2 merely discloses that a non-porous material is cut with a shear cutting method so that both lateral surfaces thereof lie at a right angle, and straightness of a lateral surface of such a non-porous material is not so important because the straightness of the non-porous material is high in the first place, unlike a porous material such as a separator. - The present invention is accomplished in view of the problem, and its object is to provide (i) a long porous separator sheet which is less likely to be torn in processing and (ii) a method for producing such a long porous separator sheet.
- In order to attain the object, in the long porous separator sheet of the present inventions a lateral surface of the long porous separator sheet has a value of R/P that is less than 1.04, where P is a linear distance between two points on a straight line in a lengthwise direction in an image of the lateral surface, and R is a distance along a shape of the lateral surface between the two points on the straight line in the lengthwise direction, the linear distance P and the distance R being obtained by binarizing the image between the long porous separator sheet and a part other than the long porous separator sheet.
- According to the configuration, the value of R/P of the lateral surface of the long porous separator sheet is less than 1.04. As such, the straightness of the lateral surface is high even though the long parous separator sheet is made of a porous material, and it is therefore possible to reduce a possibility that the long separator sheet is torn in processing.
- In order to attain the object, the method of the present invention for producing a long porous separator sheet includes the step of slitting a porous separator original sheet in a lengthwise direction of the porous separator original sheet, the slitting step including forming a lateral surface of the long porous separator sheet with use of a slitting section including an tipper blade and a lower blade which rotate in different directions, the upper blade making contact with one of two lower blades in a space formed between the two lower blades which are adjacent in a transverse direction that is perpendicular to the lengthwise direction.
- According to the method, it is possible to form the lateral surface of the long porous separator sheet whose straightness is high even though the long porous separator sheet is made of a porous material. It is therefore possible to reduce a possibility that the long separator sheet is torn in processing.
- According to an aspect of the present invention, it is possible to provide (i) a long porous separator sheet which is less likely to be torn in processing and (ii) a method for producing such a long porous separator sheet.
-
FIG. 1 is a schematic view illustrating a cross sectional configuration of a lithium-ion secondary battery. -
FIG. 2 is a schematic view illustrating details of the configuration of the lithium-ion secondary battery illustrated inFIG. 1 . -
FIG. 3 is a schematic view illustrating another configuration of the lithium-ion secondary battery illustrated inFIG. 1 . - (a) of
FIG. 4 is a schematic view illustrating a configuration of a slitting apparatus for slitting a separator original sheet, and (b) ofFIG. 4 is a view illustrating a state in which the separator original sheet is slit into a plurality of long separator sheets by the slitting apparatus. - (a) of
FIG. 5 is a view illustrating a cutting device which operates in a shear cutting mode and is provided in the slitting apparatus illustrated inFIG. 4 , (b) ofFIG. 5 is a view illustrating a slitting section which is provided in the cutting device that operates in the shear cutting mode, and (c) ofFIG. 5 is a view illustrating a state in which a separator original sheet is slit by the slitting section. -
FIG. 6 is a view illustrating a part of a lateral surface of a long separator sheet in which part straightness is evaluated. -
FIG. 7 is a view for explaining a cutting method carried out with a razor blade. - (a) of
FIG. 8 is a view for explaining a method for evaluating straightness of a lateral surface of a long separator sheet, and (b) and (c) ofFIG. 8 are views showing evaluation results of the straightness. - (a) of
FIG. 9 is a schematic view illustrating straightness of a lateral surface of a long separator sheet in accordance with the present embodiment, and (b) ofFIG. 9 is a schematic view illustrating straightness of a lateral surface of a long separator sheet which has been slit with a razor cutting method. -
FIG. 10 is a view for explaining (i) a method for measuring tensile strength of a specimen whose one lateral surface is a lateral surface of a long porous separator sheet made of polyethylene and (ii) results of the measurement. -
FIG. 11 is a view for explaining (i) a measuring method in the Charpy impact test carried out on a specimen whose one lateral surface is a lateral surface of a long porous separator sheet made of polyethylene and (ii) results of the measurement. - [Basic Configuration]
- The following description will discuss in order a lithium-ion secondary battery, a separator, a heat resistant separator, a method for producing the heat resistant separator, and a slitting apparatus.
- (Lithium-Ion Secondary Battery)
- A nonaqueous electrolyte secondary battery, typically, a lithium-ion secondary battery has a high energy density, and therefore, currently widely used not only as batteries for use in devices such as personal computers, mobile phones, and mobile information terminals, and for use in moving bodies such as automobiles and airplanes, but also as stationary batteries contributing to stable power supply.
-
FIG. 1 is a schematic view illustrating a cross sectional configuration of a lithium-ionsecondary battery 1. - As illustrated in
FIG. 1 , the lithium-ionsecondary battery 1 includes acathode 11, aseparator 12, and ananode 13. Between thecathode 11 and theanode 13, anexternal device 2 is connected outside the lithium-ionsecondary battery 1. While the lithium-ionsecondary battery 1 is being charged, electrons move in a direction A. On the other hand, while the lithium-ionsecondary battery 1 is being discharged, electrons move in a direction B. - (Separator)
- The
separator 12 is provided so as to be sandwiched between thecathode 11 which is a positive electrode of the lithium-ionsecondary battery 1 and theanode 13 which is a negative electrode of the lithium-ionsecondary battery 1. Theseparator 12 is a porous film that separates thecathode 11 and theanode 13, allowing lithium ions to move between thecathode 11 and theanode 13. Theseparator 12 contains, for example, polyolefin such as polyethylene or polypropylene as a material. -
FIG. 2 is a schematic view illustrating details of the configuration of the lithium-ionsecondary battery 1 illustrated inFIG. 1 . (a) ofFIG. 2 illustrates a normal configuration. (b) ofFIG. 2 illustrates a state in which a temperature of the lithium-ionsecondary battery 1 has risen. (c) ofFIG. 2 illustrates a state in which a temperature of the lithium-ionsecondary battery 1 has sharply risen. - As illustrated in (a) of
FIG. 2 , theseparator 12 is provided with many pores P. Normally,lithium ions 3 in the lithium-ionsecondary battery 1 can move back and forth through the pores P. - Here, there are, for example, eases in which the temperature of the lithium-ion
secondary battery 1 rises due to excessive charging of the lithium-ionsecondary battery 1, a high current caused by short-circuiting of the external device, or the like. In such cases, theseparator 12 melts or softens and the pores P are blocked as illustrated in (b) ofFIG. 2 . As a result, theseparator 12 shrinks. This stops the movement of thelithium ions 3, and consequently slops the above described temperature rise. - However, in a case where a temperature of the lithium-ion
secondary battery 1 sharply rises, theseparator 12 suddenly shrinks. In this case, as illustrated in (c) ofFIG. 2 , theseparator 12 may be destroyed. Then, thelithium ions 3 leak out from theseparator 12 which has been destroyed. As a result, thelithium ions 3 do not stop moving. Consequently, the temperature continues rising. - (Heat Resistant Separator)
-
FIG. 3 is a schematic view illustrating another configuration of the lithium-ionsecondary battery 1 illustrated inFIG. 1 . (a) ofFIG. 3 illustrates a normal configuration, and (b) ofFIG. 3 illustrates a state in which a temperature of the lithium-ionsecondary battery 1 has sharply risen. - As illustrated in (a) of
FIG. 3 , theseparator 12 can be a heat resistant separator that includes aporous film 5 and a heat resistant layer 4. The heat resistant layer 4 is laminated on a surface of theporous film 5 which surface is on acathode 11 side. Note that the heat resistant layer 4 can alternatively be laminated on a surface of theporous film 5 which surface is on ananode 13 side, or both surfaces of theporous film 5. Further, the heat resistant layer 4 is provided with, pores which are similar to the pores P. Normally, thelithium ions 3 move through the pores P and the pores of the heat resistant layer 4. The heat resistant layer 4 contains, for example, wholly aromatic polyamide (aramid resin) as a material. - As illustrated in (b) of
FIG. 3 , even in a case where the temperature of the lithium-ionsecondary battery 1 sharply rises and as a result, theporous film 5 melts or softens, the shape of theporous film 5 is maintained because the heat resistant layer 4 supports theporous film 5. Therefore, such a sharp temperature rise results in only melting or softening of theporous film 5 and consequent blocking of the pores P. This stops movement of thelithium ions 3 and consequently stops the above-described excessive discharging or excessive charging. In this way, theseparator 12 can be prevented from being destroyed. - (Production Steps of the Heat Resistant Separator)
- How to produce the heat resistant separator of the lithium-ion
secondary battery 1 is not specifically limited. The heat resistant separator can be produced by a well-known method. The following discussion assumes a case where theporous film 5 contains polyethylene as a main material. However, even in a case where theporous film 5 contains another material, the similar steps can still be applied to production of theseparator 12. - For example, it is possible to employ a method including the steps of first forming a film by adding a plasticizer to a thermoplastic resin, and then removing the plasticizer with an appropriate solvent. For example, in a case where the
porous film 5 is made of a polyethylene resin containing ultrahigh molecular weight polyethylene, it is possible to produce theporous film 5 by the following method. - This method includes (1) a kneading step of obtaining a polyethylene resin composition by kneading a ultrahigh molecular weight polyethylene and an inorganic filler such as calcium carbonate, (2) a roiling step of forming a film with the polyethylene resin composition, (3) a removal step of removing the inorganic filler from the film obtained in the step (2), and (4) a stretching step of obtaining the
porous film 5 by stretching the film obtained in the step (3). - In the removal step, many fine pores are provided in the film. The fine pores of the film stretched in the stretching step become the above-described pores P. The
porous film 5 formed as a result is a polyethylene microporous film having a predetermined thickness and a predetermined air permeability. - Note that, in the kneading step, 100 parts by weight of the ultrahigh molecular weight polyethylene, 5 parts by weight to 200 parts by weight of a low-molecular weight polyolefin having a weight-average molecular weight of 10000 or less, and 100 parts by weight to 400 parts by weight of the inorganic filler can be kneaded.
- Subsequently, in a coating step, the heat resistant layer 4 is formed on a surface of the
porous film 5. For example, on theporous film 5, an aramid/NMP (N-methylpyrrolidone) solution (coating solution) is applied, and thereby the heat resistant layer 4 that is an aramid heat resistant layer is formed. The heat resistant layer 4 can be provided on only one surface or both surfaces of theporous film 5. Alternatively, for coating, the heat resistant layer 4 can be formed by using a mixed solution containing a filler such as alumina/carboxymethyl cellulose. - A method for coating the
porous film 5 with a coating solution is not specifically limited as long as uniform wet coating can be carried out by the method. The method can be a conventionally well-known method such as a capillary coating method, a spin coating method, a slit die coating method, a spray coating method, a dip coating method, a roll coating method, a screen printing method, a flexo printing method, a bar coater method, a gravure coater method, or a die coater method. The heat resistant layer 4 has a thickness which can be controlled by adjusting (i) a thickness of a coating wet film and (ii) a solid-content concentration in the coating solution. - Note that it is possible to use a resin film, a metal belt, a metal drum, or the like as a support with which the
porous film 5 is fixed or transferred in coating. - As described above, it is possible to produce the separator 12 (heat resistant separator) in which the heat resistant layer 4 is laminated on the
porous film 5. Thus produced separator is wound on a cylindrical core. Note that a subject to be produced by the above production method is not limited to the heat resistant separator. The above production method does not necessarily include the coating step. In a case where the method includes no coating step, the subject to be produced is a separator including no heat resistant layer. - (Slitting Apparatus)
- The heat resistant separator or the separator including no heat resistant layer (hereinafter, referred to as “separator”) preferably has a width (hereinafter, referred to as “product width”) suitable for application products such as the lithium-ion
secondary battery 1. However, for improving productivity, the separator is produced so as to have a width that is equal to or larger than a product width. This is referred to as a separator original sheet. After the separator original sheet is once produced, the separator original sheet is cut (slit) by the slitting apparatus so that a “separator width” (which means a length in a direction substantially perpendicular to a lengthwise direction and a thickness direction) of the separator original sheet becomes the product width, and thus a long separator sheet is obtained. - In the following descriptions, a wide separator which is before being slit is referred to as “separator original sheet”, and a separator which has been slit so as to have a separator width that is the product width is particularly referred to as “long separator sheet”. Note that “slitting” means to slit the separator original sheet in the lengthwise direction (i.e., a flow direction of the film during production; MD: machine direction), and that “cutting” means to cut the long separator sheet in a transverse direction (TD). The “transverse direction (TD)” means a direction which is substantially perpendicular to the lengthwise direction (MD) and the thickness direction of the long separator sheet.
- (Configuration of Slitting Apparatus)
- (a) of
FIG. 4 is a schematic view illustrating a configuration of aslitting apparatus 6 which includes acutting device 7 that operates in a shear cutting mode. (b) ofFIG. 4 is a view illustrating a state in which an original sheet 12O of a separator (porous separator) is slit into long separator sheets (long porous separator sheets) 12 a and 12 b by theslitting apparatus 6. -
Embodiment 1 exemplifies the separator original sheet 12O in which a wholly aromatic polyamide (aramid resin) as the heat resistant layer 4 is laminated on one surface of theporous film 5, as illustrated inFIG. 3 . Note, however, thatEmbodiment 1 is not limited to this, and the separator original sheet 12O can be aporous film 5 on which no heat resistant layer 4 is laminated or can be a sheet in which heat resistant layers 4 are laminated on both surfaces of theporous film 5. - As illustrated in (a) of
FIG. 4 , theslitting apparatus 6 includes a wind-offroller 63 which is rotatably supported and has a cylindrical shape,rollers first touch roller 81U, asecond touch roller 81L, afirst arm 82U, asecond arm 82L, a first take-up assistingroller 83U, a second take-up assistingroller 83L, a first winding-uproller 70U, a second winding-uproller 70L, and thecutting device 7. - In the
slitting apparatus 6, a cylindrical core c is attached onto the wind-offroller 63, and the separator original sheet 12O is wound on the core c. The separator original sheet 12O is wound off from the core c along a route U or L. In a case where the separator original sheet 12O is to be transferred while a surface A of the separator original sheet 12O serves as an upper surface, the separator original sheet 12O is wound off along the route L. Whereas, in a case where the separator original sheet 12O is to be transferred while a surface B of the separator original sheet 12O serves as an upper surface, the separator original sheet 12O is wound off along the route U. Note that, inEmbodiment 1, the separator original sheet 12O is transferred while the surface A serves as an upper surface, and therefore the separator original sheet 12O is wound off along the route L. - In
Embodiment 1, the surface A is a surface of theporous film 5 which surface is opposite to a surface making contact with the heat resistant layer 4, and the surface B is a surface of the heat resistant layer 4 which surface is opposite to a surface making contact with theporous film 5. - The separator original sheet 12O which has been thus wound off is transferred to the
cutting device 7 via theroller 64 and theroller 65, and is then slit intolong separator sheets FIG. 4 ). - (Cutting Device and Slitting Section)
- (a) of
FIG. 5 is a view illustrating thecutting device 7 which operates in a shear cutting mode and is provided in theslitting apparatus 6 illustrated inFIG. 4 . (b) ofFIG. 5 is a view illustrating a slitting section S provided in thecutting device 7. (c) ofFIG. 5 is a view illustrating a state in which the separator original sheet 12O is slit by the slitting section S of thecutting device 7. - As illustrated in (a) of
FIG. 5 , thecutting device 7 which operates in a shear cutting mode includes ashaft 66 and ashaft 67 each of which has a cylindrical shape. Theshaft 66 and theshaft 67 are supported so as to rotate in different directions and are located on a lower side and on an upper side, respectively. Theshaft 67 which is on the upper side is provided with a plurality (8 in Embodiment 1) ofupper blades 67 a each of which is a circular blade. As illustrated in (b) ofFIG. 5 , the plurality ofupper blades 67 a each of which is a circular blade are inserted into respective of a plurality (8 in Embodiment 1) of spaces which are provided in theshaft 66 located on the lower side. Note that, as illustrated in (a) ofFIG. 5 , thecutting device 7 which operates in the shear cutting mode includes a plurality (8 in Embodiment 1) of slitting sections S. - As illustrated in (c) of
FIG. 5 , each of the slitting sections S, which are provided in thecutting device 7 that operates in the shear cutting mode, includes (i) theupper blade 67 a, (ii)lower blades 66 a which are adjacent to each other in the transverse direction (TD) that is perpendicular to the lengthwise direction (MD), and (iii) aspace 66 b that is provided between thelower blades 66 a which are adjacent, to each other. Note that thelower blades 66 a and thespace 66 b are provided in theshaft 66 that is located on the lower side. - In each of the slitting sections S, the
upper blade 67 a is inserted into thespace 66 b and makes contact with a lateral surface of one of the adjacent twolower blades 66 a which one is located on a left side in (c) ofFIG. 5 . - An edge part of the
upper blade 67 a has aflat part 67 b and aninclined part 67 c. Theflat part 67 b is a part which is to make contact with thelower blade 66 a. Theinclined part 67 c is opposite to theflat part 67 b and is inclined so that, the edge part of theupper blade 67 a gradually becomes sharper toward a tip of theupper blade 67 a. - Note that, in
Embodiment 1, an example is described in which the edge part of theupper blade 67 a has a cross section in which only one side is inclined but the edge part of theupper blade 67 a can have a cross section of a rocking shear, or the like. - In a case where the separator original sheet 12O is slit by the slitting section S thus configured, each of the
long separator sheets lateral surface 12 c that is shaped by thetipper blade 67 a (specifically, theinclined part 67 c of theupper blade 67 a) and thespace 66 b and (ii) alateral surface 12 d that is shaped by theupper blade 67 a (specifically, theflat part 67 b of thetipper blade 67 a) and thelower blade 66 a with which theupper blade 67 a contacts. - In
Embodiment 1, in order to inhibit, the heat resistant layer 4 from being peeled off, theupper blade 67 a. is brought into contact with the surface A, i.e., the surface of theporous film 5 which surface is opposite to the surface making contact with the heat resistant layer 4. Note, however, thatEmbodiment 1 is not limited to this. - Moreover, an angle at which the
upper blade 67 a makes contact with thelower blade 66 a and a pressure with which theupper blade 67 a makes contact with thelower blade 66 a can be appropriately adjusted to he an angle and a pressure which are suitable for producing thelong separator sheets - Among the plurality of
long separator sheets cutting device 7, each of thelong separator sheets 12 a is transferred via theroller 68U, theroller 69U, and the first take-up assistingroller 83U, and is then wound on a cylindrical core u (bobbin) that is attached onto the first winding-uproller 70U. Moreover, each of thelong separator sheets 12 b among the plurality oflong separator sheets roller 68L, theroller 69L, and the second take-up assistingroller 83L, and is then wound on a cylindrical core 1 (bobbin) that is attached onto the second winding-uproller 70L, Note that thelong separator sheets - In the separator rolls 12U and 12L, the
long separator sheets long separator sheets long separator sheets - In
Embodiment 1, as illustrated in (b) ofFIG. 4 , the separator original sheet 12O is slit, into sevenlong separator sheets long separator sheets 12 a and three even-numberedlong separator sheets 12 b are obtained. The four odd-numberedlong separator sheets 12 a are wound on the respective cylindrical cores u (bobbin) which are attached onto the first winding-uproller 70U, and the three even-numberedlong separator sheets 12 b are wound on the respective cylindrical cores 1 (bobbin) which are attached onto the second winding-uproller 70L. Note, however, thatEmbodiment 1 is not limited to this example, and it is of course possible to appropriately change the number of thelong separator sheets long separator sheets long separator sheets Embodiment 1, long separator sheets which are obtained on both ends by the slitting with use of the eight slitting sections S are not used. - In
Embodiment 1, an example is described in which the number of long separator sheets that are wound on the respective cylindrical cores u (bobbin) provided on the first winding-uproller 70U is different from the number of long separator sheets that are wound on the respective cylindrical cores 1 (bobbin) provided on the second winding-tip roller 70L. Note, however, that the number of long separator sheets that are wound on the respective cylindrical cores u can be identical with the number of long separator sheets that are wound on the respectivecylindrical cores 1. - (Winding-Up Section)
- On the first winding-up
roller 70U (winding-up section), four cores u are detachably provided in accordance with the number of thelong separator sheets 12 a, i.e., the four odd-numberedlong separator sheets 12 a. Similarly, on the second winding-uproller 70L (winding-up section), threecores 1 are detachably provided in accordance with the number of thelong separator sheets 12 b, i.e., the three even-numberedlong separator sheets 12 b. - As illustrated in (a) of
FIG. 4 , the first winding-uproller 70U rotates in a direction indicated by the arrow in (a) ofFIG. 4 together with the core u so as to wind up thelong separator sheet 12 a (winding-up step). The core u can be detached from the first winding-uproller 70U together with thelong separator sheet 12 a which has been wound on the core u. - Similarly, the second winding-up
roller 70L rotates in a direction indicated by the arrow in (a) ofFIG. 4 together with thecore 1 so as to wind up thelong separator sheet 12 b (winding-up step). Thecore 1 can be detached from the second winding-uproller 70L together with thelong separator sheet 12 b which has been wound on thecore 1. - (Touch Roller)
- As illustrated in (a) of
FIG. 4 , thefirst touch roller 81U in theslitting apparatus 6 is rotatably provided at (i.e., fixed to) one end of thefirst arm 82U, and thesecond touch roller 81L in theslitting apparatus 6 is rotatably provided at (i.e., fixed to) one end of thesecond arm 82L. Thefirst arm 82U can swing on arotary shaft 84U (shaft) that is provided at the other end of thefirst arm 82U, and thesecond arm 82L can swing on arotary shaft 84L (shaft) that is provided at the other end of thesecond arm 82L (in respective directions indicated by arrows in (a) ofFIG. 4 ). The first take-up assistingroller 83U is provided between thefirst touch roller 81U and therotary shaft 84U of thefirst arm 82U and is rotatably fixed to thefirst arm 82U. The second take-tip assisting roller 83L is provided between thesecond touch roller 81L and therotary shaft 84L of thesecond arm 82L and is rotatably fixed to thesecond arm 82L. - Note that the first and
second touch rollers long separator sheets second touch rollers long separator sheets second touch rollers second touch rollers long separator sheets second touch rollers second touch rollers - (Straightness Evaluation of Lateral Surface of Long Separator Sheet)
-
FIG. 6 is a view illustrating a part of a lateral surface of each of thelong separator sheets - In
Embodiment 1, as illustrated in (a) ofFIG. 6 , straightness of thelateral surface 12 c (indicated by A in (a) ofFIG. 6 ) of each of thelong separator sheets lateral surface 12 c which part makes contact with the surface B was evaluated. - This part corresponds of an edge part (indicated by A in (b) of
FIG. 6 ) of the separator rolls 12U and 12L, and also corresponds to a part A of each of thelong separator sheets FIG. 6 . - Note that, in the straightness evaluation of the lateral surface of the long separator sheet, a long separator sheet which had been obtained by slitting the separator original sheet 12O with a razor blade (later described) was also used as Comparative Example, in addition to (i) a long separator sheet which had been obtained by slitting the
porous film 5, which had no heat resistant layer 4, with thecutting device 7 that operates in the shear cutting mode and (ii) thelong separator sheets cutting device 7 that operates in the shear cutting mode. -
FIG. 7 is a view for explaining a conventional cutting (slitting) method carried out with a razor blade. - As illustrated in
FIG. 7 , the separator original sheet 12O is transferred to aroller 101. Theroller 101 has a groove into which an edge of arazor blade 100 can be partially inserted. With the configuration, the separator original sheet 12O is slit into long separator sheets by therazor blade 100 and the groove. - (a) of
FIG. 8 is a view for explaining a method for evaluating straightness of a lateral surface of a long separator sheet. (b) ofFIG. 8 is a view showing results of straightness evaluation on a lateral surface of a long separator sheet (here, referred to as “polyolefin separator”) which has been obtained by slitting theporous film 5, which has no heat resistant layer 4, with the shear cutting method illustrated inFIG. 5 . (c) ofFIG. 8 is a view showing results of straightness evaluation on thelateral surface 12 c of each of thelong separator sheets porous film 5, with the razor cutting method illustrated inFIG. 7 and the shear cutting method illustrated inFIG. 5 . - The following description will discuss a method for evaluating straightness of a lateral surface of a long separator sheet, with reference to an example method for evaluating straightness of the
lateral surface 12 c of each of thelong separator sheets - As illustrated in (a) of
FIG. 8 , first, an original image of thelateral surface 12 c is obtained. - Note that a lower part of the original image illustrated in (a) of
FIG. 8 is a surface B side of each of thelong separator sheets FIG. 6 . - Subsequently, the original image is binarized into each of the
long separator sheets long separator sheets - By this binarization, it is possible to obtain a processed image in which each of the
Jong separator sheets long separator sheets - In the processed image, the part other than each of the
long separator sheets - Based on this, a value of “edge length (R)/longer side length (P)” was calculated, and thus straightness of the lateral surface of the long separator sheet was evaluated.
- Specifically, with use of analysis software “WinROOF (MITANI CORPORATION)”, a value of “edge length (R)/longer side length (P)” was obtained through the following processes 1. through 6.
- 1. Read in the original image.
- 2. Separate the original image into three colors, i.e., green, red, and blue by color separation.
- 3. Extract a background by carrying out automatic binarization on a green image obtained by the color separation (discriminant analysis method: modal method).
- 4. Measure a peripheral length (O+P+Q+R) of a region extracted in the above 3.
- 5. Measure a three-side line length (O+P+Q) of the region extracted in the above 3., the three-side line length (O+P+Q) excluding an interface between the sample and the background.
- 6. Subtract the three-side line length (O+P+Q) measured in the above 5. from the peripheral length (Q+P+Q+R) measured in the above 4., and thus calculate an edge length (R).
- 7. Divide the calculated edge length (R) by the longer side length (P).
- The longer side length (P) corresponds to a linear distance between two points on a straight line along the MD on the
lateral surface 12 c, and the edge length (R) corresponds to a distance which is along a shape of thelateral surface 12 c between the two points on the straight line along the MD. - In a case where the value of “edge length (R)/longer side length (P)” is large, this means that distortion in a direction perpendicular to the MD is large. Meanwhile, in a case where the value is small, this means that distortion in the direction perpendicular to the MD is small.
- Note that, in order to reduce a possibility that the long separator sheet is torn during processing, the value of “edge length (R)/longer side length (P)” needs to be less than 1.04.
- As illustrated in (b) of
FIG. 8 , in the case of the long separator sheet (here, referred to as “polyolefin separator”) which has been obtained by slitting theporous film 5, which has no heat resistant layer 4, with the shear cutting method illustrated inFIG. 5 , the value of “edge length (R)/longer side length (P)” was 1.007, which was near to an ideal value, i.e., 1. - From the above result, in the case of the porous film 5 (polyolefin separator) including no heat resistant layer 4, the sufficiently satisfactory straightness of the lateral surface of the long separator sheet could be obtained.
- On the other hand, in the case of the long separator sheet (here, referred to as laminated separator) which had been obtained by slitting the separator original sheet 12O, in which wholly aromatic polyamide (aramid resin) was laminated as the heat resistant layer 4 on one surface of the
porous film 5, with the razor cutting method illustrated inFIG. 7 , the value of “edge length (R)/longer side length (P)” was 1.047, which was greatly different from the ideal value, i.e., 1 (see (c) ofFIG. 8 ). - As such, from the viewpoint of reducing the possibility of being torn during processing, the long separator sheet (laminated separator) which is obtained by slitting the separator original sheet 12O, in which wholly aromatic polyamide (aramid resin) is laminated as the heat resistant layer 4 on one surface of the
porous film 5, with the razor cutting method illustrated inFIG. 7 is not preferable. - In the case of the each of the
long separator sheets porous film 5, with the shear cutting method illustrated inFIG. 5 , the value of “edge length (R)/longer side length (P)” was the ideal value, i.e., 1. - From the above results, in the cases of (i) the separator original sheet 12O in which wholly aromatic polyamide (aramid resin) as the heat resistant layer 4 is laminated on one surface of the
porous film 5 and (ii) the separator original sheet in which wholly aromatic polyamide (aramid resin) as the heat resistant layer 4 is laminated on both surfaces of theporous film 5, it is necessary to carry out the slitting with the shear cutting method illustrated inFIG. 5 in order to obtain satisfactory straightness of the lateral surface of the long separator sheet. - (a) of
FIG. 9 is a schematic view illustrating the straightness of thelateral surface 12 c of each of thelong separator sheets porous film 5, with the shear cutting method illustrated inFIG. 5 . (b) ofFIG. 9 is a schematic view illustrating the straightness of alateral surface 12 c′ of each oflong separator sheets 12 a′ and 12 b′ (laminated separator) which has been obtained by slitting the separator original sheet 12O, in which wholly aromatic polyamide (aramid resin) is laminated as the heat resistant layer 4 on one surface of theporous film 5, with the razor cutting method illustrated inFIG. 7 . - As illustrated in
FIG. 9 , from the viewpoint of reducing the possibility of being torn during processing, thelong separator sheets long separator sheets 12 a′ and 12 b′ having the low straightness of the lateral surface. - (Measurement of Tensile Strength)
- The following description will discuss, with reference to
FIG. 10 , (i) a method for measuring tensile strength of a long separator sheet which has each of the values of R/P shown in (c) ofFIG. 8 and in which the heat resistant layer 4 is laminated on one surface of theporous film 5 and (ii) results of the measurement. Specifically, the following description will discuss (i) a method for measuring tensile strength of each oflong separator sheets 12 a″ and 12 b″ in which wholly aromatic polyamide (aramid resin) as the heat resistant layer 4 is laminated on one surface of a poly olefin separator which is theporous film 5 and (ii) results of the measurement. -
FIG. 10 is a view for explaining (i) a method for measuring tensile strength of aspecimen 12 e whose one lateral surface is alateral surface 12 c″ of each of thelong separator sheets 12 a″ and 12 b″ which are wound into respective separator rolls 12U″ and 12L″. - The separator rolls 12U″ and 12L″ illustrated, in (a) of
FIG. 10 are obtained by winding 200 m of the respectivelong separator sheets 12 a″ and 12 b″ on respective cores u and l having a diameter of 3 inches. Here, thelong separator sheets 12 a″ and 12 b″ have been obtained by slitting a separator original sheet, in which wholly aromatic polyamide as a heat resistant layer is laminated on one surface of a porous film made of polyethylene, in a lengthwise direction (MD) of the original sheet. - The
specimen 12 e has been prepared by cutting, with use of a cutter, out from each of thelong separator sheets 12 a″ and 12 b″ so as to include, as one lateral surface, thelateral surface 12 c″ of each of thelong separator sheets 12 a″ and 12 b″ and to have a size of 1 cm (width)×5 cm (length). - As illustrated in (b) of
FIG. 10 , upper and lower parts (each having a length of 1.5 cm) of thespecimen 12 e are placed on respective chucks (holding base) 14 a and 14 b, and a distance between thechuck 14 a and thechuck 14 b is 2 cm. - Note that the tensile strength was measured based on “JIS K 7161 Plastics-Determination of tensile properties”. The followings are concrete measuring device and measurement conditions which were employed.
- Device: TENSILON Universal Material Testing Instrument (A&D Company, Limited, Type RTF-1210)
- Specimen: 5 cm×1 cm
- Test speed (speed of
chuck 14 a): 100 mm/mm - Number of measurement: 3 times
- Chuck-to-chuck distance: 2 cm
- Test direction: Lengthwise direction (MD) of long separator sheet
- A tensile strength X (MPa) was calculated from a stress A (N) with which the
specimen 12 e was torn. Specifically, the tensile strength X (MPa) was calculated based on the following (Formula 1): -
Tensile strength X (MPa)−load A (N)/(width of specimen (mm)×film thickness of specimen (mm) (Formula 1) - As illustrated in (c) of
FIG. 10 , as compared with specimens (edge length (R)/longer side length (P): 1,047; razor n=1, razor n=2, razor n=3) obtained from a long separator sheet which has been obtained by slitting, with the razor cutting method, a separator original sheet, in which wholly aromatic polyamide as a heat resistant layer is laminated on one surface of a porous film, made of polyethylene, it is found that the load (N) with which thespecimens 12 e (edge length (R)/longer side length (P): 1.000; shear cutting n=1, shear cutting n=2, shear cutting n=3) were torn is larger. - As shown in (d) of
FIG. 10 , an average tensile strength X (MPa) of the specimens (razor n=1, razor n=2, razor n=3) is 2.12 Mpa, and an average tensile strength X (MPa) of thespecimens 12 e (shear cutting n=1, shear cutting n=2, shear cutting n=3) is 224 Mpa. From these results, the tensile strength of thespecimens 12 e each having the lateral surface obtained by slitting with the shear cutting is evidently larger than the tensile strength of the specimens each having the lateral surface obtained by slitting with the razor cutting method. - A larger tensile strength means to be tougher against stretching. In a case where a slit lateral surface is uneven as in the specimens having the lateral surface obtained by slitting with the razor cutting method, concentration of stress occurs in stretching, and accordingly breaking may be more likely to occur.
- (Charpy Impact Test)
- The following description will discuss, with reference to
FIG. 11 , (i) a measuring method in the Charpy impact test on a long separator sheet which has each of the values of: R/P shown in (c) ofFIG. 8 and in which the heat resistant layer 4 is laminated on one surface of theporous film 5 and (ii) results of the measurement. Specifically, the following description will discuss (i) a measuring method in the Charpy impact test on each oflong separator sheets 12 a″ and 12 b″ in which wholly aromatic polyamide (aramid resin) as the heat resistant layer 4 is laminated on one surface of a polyolefin separator which is theporous film 5 and (ii) results of the measurement. -
FIG. 11 is a view for explaining (i) a measuring method in the Charpy impact test on aspecimen 12 f whose one lateral surface is alateral surface 12 c″ of each of thelong separator sheets 12 a″ and 12 b″ which are wound into respective separator rolls 12U″ and 12L″. - The separator rolls 12U″ and 12L″ illustrated in (a) of
FIG. 11 are obtained by winding 200 m of the respectivelong separator sheets 12 a″ and 12 b″ on respective cores u and l having a diameter of 3 inches. Here, thelong separator sheets 12 a″ and 12 b″ have been obtained by slitting a separator original sheet, in which wholly aromatic polyamide as a heat resistant layer is laminated on one surface of a porous film made of polyethylene, in a lengthwise direction (MD) of the original sheet. - The
specimen 12 f has been prepared by cutting, with use of a cutter, out from each of thelong separator sheets 12 a″ and 12 b″ so as to include, as one lateral surface, thelateral surface 12 c″ of each of thelong separator sheets 12 a″ and 12 b″ and to have a size of 1 cm (width)×8 cm (length). - Note that the Charpy impact test was carried out based on “JIS K 7111-1 Plastics-Determination of Charpy impact properties”. The followings are concrete measuring device and measurement conditions which were employed.
- Device: UNIVERSAL IMPACT TESTER (YASUDA SEIKI SEISAKUSHO, LTD., No. 258)
- Specimen: 8 cm×1 cm
- Lifting angle: 150°
- Number of measurement: 5 times
- Pendulum (hammer) capacity: 1 J
- Number of specimen: 1 sheet
- Notch in specimen: None
- Test direction: Transverse direction (TD)
- Note that, normally, a notch is provided in a specimen for the Charpy impact test. However, in this experiment, a shape itself of a slit edge part of a specimen is evaluated, and therefore no notch is additionally provided in the sample which has been cut out in a rectangular shape.
- (b) of
FIG. 11 is a schematic view for explaining a measuring method in the Charpy impact test on thespecimen 12 f, and (c) ofFIG. 11 is a view showing results of the Charpy impact test on thespecimen 12 f. - As illustrated in (b) of
FIG. 11 , a pendulum (hammer) 15 which is heavy is swung down onto thespecimen 12 f from a height h′, and then thependulum 15 breaks thespecimen 12 f and is then swung up to a height h. Note that a distance k is a distance between a rotation center of thependulum 15 and a center of gravity of thependulum 15. - An angle α in (b) of
FIG. 11 does not change in accordance with replacement of the specimen, and indicates a lifting angle. Meanwhile, an angle β in (b) ofFIG. 11 is an angle of thependulum 15. The angle (β) of thependulum 15 becomes smaller when energy consumed to break the specimen is larger, and the angle (β) of thependulum 15 becomes larger when energy consumed to break the specimen is smaller. - That is, the
pendulum 15 is swung down from the predetermined height h′ regardless of types of the specimen, and therefore initial energy (potential energy) of thependulum 15 is constant. From this, the angle (β) of thependulum 15 represents residual energy obtained by subtracting, from the initial energy, energy consumed to break the specimen. - As illustrated in (c) of
FIG. 11 , an average angle (β) of thependulum 15 in the 5-time trials was 114.9° in regard to the specimens (edge length (R)/longer side length (P): 1.000) which had been obtained from the long separator sheet obtained by slitting, with the shear cutting method, the separator original sheet in which wholly aromatic polyamide as the heat resistant layer was laminated on one surface of the porous film made of polyethylene. Meanwhile, an average angle (β) of thependulum 15 in the 5-time trials was 117.4° in regard to the specimens (edge length (R)/longer side length (P): 1.047) which had been obtained from the long separator sheet obtained by slitting, with the razor cutting method, the separator original sheet in which wholly aromatic polyamide as the heat resistant layer was laminated on one surface of the porous film made of polyethylene. - From the above results, it is found that the specimen having the lateral surface with inferior straightness is easily broken, as compared with the
specimen 12 f having the lateral surface with high straightness. - [Main Points]
- In the long porous separator sheet in accordance with an
aspect 1 of the present invention, a lateral surface of the long porous separator sheet has a value of R/P that is less than 1.04, where P is a linear distance between two points on a straight line in a lengthwise direction in an image of the lateral surface, and R is a distance along a shape of the lateral surface between the two points on the straight line in the lengthwise direction, the linear distance P and the distance R being obtained by binarizing the image between the long porous separator sheet and a part other than the long porous separator sheet. - According to the configuration, the value of R/P of the lateral surface of the long porous separator sheet is less than 1.04. As such, the straightness of the lateral surface is high even though the long porous separator sheet is made of a porous material, and it is therefore possible to reduce a possibility that the long separator sheet is torn in processing.
- The long porous separator sheet in accordance with an
aspect 2 of the present invention can include, in theaspect 1, a plurality of layers. - According to the configuration, it is possible to provide the long porous separator sheet which is made up of a plurality of layers.
- In the long porous separator sheet in accordance with an
aspect 3 of the present invention, it is possible in theaspect 2 that the plurality of layers are a porous film layer and a porous heat resistant layer which is laminated on one surface of the porous film layer. - According to the configuration, it is possible to provide the long porous separator sheet in which the porous heat resistant layer is laminated on the one surface.
- In the long porous separator sheet in accordance with art aspect 4 of the present invention, it is possible in the
aspect 2 that the plurality of layers are a porous film layer and porous heat resistant layers which are laminated on both surfaces of the porous film layer. - According to the configuration, it is possible to provide the long porous separator sheet in which the porous heat resistant layers are laminated on the both surfaces.
- In the long porous separator sheet in accordance with an
aspect 5 of the present invention, it is possible in any one of theaspects 1 through 4 that the lateral surface of the long porous separator sheet is obtained by being slit in a slitting section including an upper blade and a lower blade which rotate in different directions, the upper blade making contact with one of two lower blades in a space formed between the two lower blades which are adjacent in a transverse direction that is perpendicular to the lengthwise direction. - According to the configuration, it is possible to provide the long porous separator sheet whose lateral surface has high straightness.
- The porous separator roll in accordance with an
aspect 6 of the present invention is configured by winding, on a core, the long porous separator sheet described in any one of theaspects 1 through 5. - According to the configuration, it is possible to provide the porous separator roll obtained by winding, on a core, the long porous separator sheet whose lateral surface has high straightness.
- The lithium-ion battery in accordance with an
aspect 7 of the present invention is configured to include a porous separator which has been obtained by cutting, in a predetermined length, the long porous separator sheet described in any one of theaspects 1 through 5 in a transverse direction that is perpendicular to the lengthwise direction. - According to the configuration, it is possible to provide the lithium-ion battery which includes the porous separator whose lateral surface has high straightness.
- The method in accordance with an
aspect 8 of the present invention for producing a long porous separator sheet includes the step of slitting a porous separator original sheet in a lengthwise direction of the porous separator original sheet, the slitting step including forming a lateral surface of the long porous separator sheet with use of a slitting section including an upper blade and a lower blade which rotate in different directions, the upper blade making contact with one of two lower blades in a space formed between the two lower blades which are adjacent in a transverse direction that is perpendicular to the lengthwise direction. - According to the method, it is possible to form the lateral surface of the long porous separator sheet whose straightness is high even though the long porous separator sheet is made of a porous material. It is therefore possible to reduce a possibility that the long separator sheet is torn in processing.
- [Additional Remarks]
- The present invention is not limited to the embodiments, but can be altered by a skilled person in the art within the scope of the claims. An embodiment derived from a proper combination of technical means each disclosed in a different embodiment is also encompassed in the technical scope of the present invention. Further, it is possible to form a new technical feature by combining the technical means disclosed in the respective embodiments.
- The present invention can be used in a long porous separator sheet, a method for producing the long porous separator sheet, a roll of the long porous separator sheet, a lithium-ion battery, and the like.
-
- 1: Lithium-ion secondary battery
- 4: Heat resistant layer (porous heat resistant layer)
- 5: Porous film (porous film layer)
- 6: Slitting apparatus
- 7: Cutting device
- 12: Separator (porous separator)
- 12 a: Long separator sheet (long porous separator sheet)
- 12 b: Long separator sheet (long porous separator sheet)
- 12 c: Lateral surface
- 12 d: Lateral surface
- 12 a″: Long separator sheet (long porous separator sheet)
- 12 b″: Long separator sheet, (long porous separator sheet)
- 12 c″: Lateral surface
- 12 d″: Lateral surface
- 12U: Separator roll (porous separator roll)
- 12L: Separator roll (porous separator roll)
- 12U″: Separator roll (porous separator roll)
- 12L″: Separator roil (porous separator roll)
- 12O: Separator original sheet (porous separator original sheet)
- 66: Lower shaft
- 66 a: Lower blade
- 66 b: Space
- 67: Upper shaft
- 67 a: Upper blade
- 67 b: Flat part
- 67 c: Inclined part
- 1: Core
- u: Core
- MD: Lengthwise direction of long separator sheet or separator original sheet
- TD: Transverse direction of long separator sheet or separator original sheet
- S: Slitting section
- Surface A: Surface of porous film which surface is opposite to surface making contact with heat resistant layer
- Surface B: Surface of heat resistant layer which surface is opposite to surface making contact with porous film
- O: Left side length
- P: Longer side length (linear distance between two points on straight line in lengthwise direction)
- Q: Right side length
- R: Edge length (distance along shape of lateral surface between two points on straight line in lengthwise direction)
Claims (8)
Applications Claiming Priority (1)
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PCT/JP2016/062185 WO2017179214A1 (en) | 2016-04-15 | 2016-04-15 | Porous separator long body, manufacturing method for same, wound body, and lithium ion battery |
Publications (2)
Publication Number | Publication Date |
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US20190027726A1 true US20190027726A1 (en) | 2019-01-24 |
US10727463B2 US10727463B2 (en) | 2020-07-28 |
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US15/312,916 Active US10727463B2 (en) | 2016-04-15 | 2016-04-15 | Long porous separator sheet, method for producing the same, roll, and lithium-ion battery |
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Country | Link |
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US (1) | US10727463B2 (en) |
JP (1) | JP6381652B2 (en) |
KR (1) | KR101807445B1 (en) |
CN (1) | CN107529343B (en) |
WO (1) | WO2017179214A1 (en) |
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US10727463B2 (en) | 2020-07-28 |
KR20170126780A (en) | 2017-11-20 |
KR101807445B1 (en) | 2017-12-08 |
JPWO2017179214A1 (en) | 2018-04-19 |
CN107529343B (en) | 2019-12-10 |
JP6381652B2 (en) | 2018-08-29 |
CN107529343A (en) | 2017-12-29 |
WO2017179214A1 (en) | 2017-10-19 |
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